Trk's are high affinity binding protein kinase receptors that are activated by Neurotrophins (NT), a group of soluble growth factors including Nerve Growth Factor (NGF), Brain-Derived Neurotrophic Factor (BDNF) and Neurotrophin 3-5 (NT 3-5). The Trk's consist of three family members TrkA, TrkB and TrkC that bind to and mediate the signal transduction derived from the Neurotrophins. NGF activates TrkA, BDNF and NT-4/5 activate TrkB and NT3 activates TrkC.
Inhibitors of the Trk/neutrophin pathway have been demonstrated to be highly effective in numerous pre-clinical animal models of pain. Antagonistic NGF and TrkA antibodies have been shown to be efficacious in inflammatory and neuropathic pain animal models and in human clinical trials. See Woolf, C. J. et al. (1994) Neuroscience 62, 327-331; Zahn, P. K. et al. (2004) J. Pain 5, 157-163; McMahon, S. B. et al., (1995) Nat. Med. 1, 774-780; Ma, Q. P. and Woolf, C. J. (1997) Neuroreport 8, 807-810; Shelton, D. L. et al. (2005) Pain 116, 8-16; Delafoy, L. et al. (2003) Pain 105, 489-497; Lamb, K. et al. (2003) Neurogastroenterol. Motil. 15, 355-361; and Jaggar, S. I. et al. (199) Br. J. Anaesth. 83, 442-448. Through gene disruption studies in mice the TrkA-NGF interaction was found to be required for the survival of certain peripheral neuron populations involved in mediating pain signaling in the case of pancreatic cancer—an increase in the expression of TrkA was shown to correlate with an increase level of pain signaling (Zhu et al., Journal of Clinical oncology, 17:2419-2428 (1999)). Increased expression of NGF and TrkA was also observed in human osteoarthritis chondrocytes (Iannone et al, Rheumatology 41:1413-1418 (2002)). In particular, anti-TrkA antibodies and anti-NGF antibodies have been demonstrated to be effective analgesics in in vivo models of inflammatory and neuropathic pain. See WO2006/131952, WO2005/061540, EP1181318 and WO01/78698, WO2004/058184 and WO2005/019266, respectively. See also WO2004/096122 and WO2006/137106 which describe the use of an anti-TrkA antibody in combination with an opioid analgesic for the treatment or prevention of pain.
Trk inhibitors that can induce apoptosis of proliferating osteoblast may be useful in treating diseases related to an imbalance of the regulation of bone remodeling, such as osteoporosis, rheumatoid arthritis and bone metastases. The expression of TrkA and TrkC receptors in the bone forming area in mouse models of bone fracture and localization of NGF in almost all bone forming cells have been observed (K. Asaumi, et al., Bone (2000) 26(6) 625-633). See also Exper Opin. Ther. Patents (2009) 19(3)), WO2006/115452 and WO2006/087538, WO6123113, WO10033941, WO10077680, WO2005110994, Investigational New Drugs (2004), 22, 449-458 and R. Tripathy, et al., Bioorg. Med. Chem. Lett., 2008, 18, 3551-3555. The association between overexpression, activation, amplification and/or mutation of Trks and several cancers as seen with studies conduct on neuroblastoma (Brodeur, G. M., Nat. Rev. Cancer 2003, 3, 203-216), ovarian cancer (Kruettgen et al., Brain Pathology 2006, 16: 304-310), prostate cancer (Dionne et al., Clin. Cancer Res. 1998, 4(8): 1887-1898), pancreatic cancer (Dang et al., J of Gastroenterology and Hepatology 2006, 21(5): 850-858), large cell neuroendocrine tumors (Marchetti et al., Human Mutation 2008, 29(5), 609-616, and colorectal cancer (Bardelli, A., Science 2003, 300, 949) support the reasoning that therapeutic implications of an effective Trk inhibitor may extend far beyond pain therapy. See also WO2005/030128, WO2012158413, WO07013673, WO07025540, WO08052734, WO2012028579, WO2012159565, WO2012107434, WO2012003387, WO2010111653, WO2008124610, WO2004098518, EP1388341, WO2012028579, WO2008003770, WO2012161879, WO2012100223, WO2009046802, WO2009003999, WO2007042321, US2005143384, WO2009003998, WO2007069773, WO2005/030128, US2010120862.
Also promising is the utility of Trk inhibitors in the treatment of inflammatory lung diseases such as asthma (Freund-Michel, V; et al., Pharmacology & Therapeutics (2008), 117(1), 52-76), interstitial cystitis (Hu Vivian Y; et. al., J of Urology (2005, 173(3), 1016-21), inflammatory bowel disease including ulcerative colitis and Crohn's disease (Di Mola, F. F., et al., Gut (2000), 46(5), 670-678 and inflammatory skin diseases such as atopic dermatitis (Dou, Y. C., et. Al., Archives of Dermatological Research (2006), 298(1), 31-37, eczema and psoriasis (Raychaudhuri, S. P. et. al., J of Investigative Dermatology (2004), 122(3), 812-819).
Modulation of the neutrophin/Trk pathway also has been shown to have an effect in the etiology of neurodegenerative diseases including multiple sclerosis, Parkinson's disease and Alzheimer's disease (Sohrabji, et. al., Neuroendocrinology (2006), 27(4), 404-414).
Thus, the compounds of the invention, which are Trk inhibitors, are believed to be useful in the treatment of multiple types of acute and chronic pain including but not limited to inflammatory pain, neuropathic pain, and pain associated with cancer, surgery and bone fracture. The compounds may also be useful in the treatment of cancer, inflammation, neurodegenerative diseases and certain infectious diseases.